What are the main causes of oxygen presence in gas pipeline

[engr2GW]

Hello all,
I saw a situation where oxygen analyzer was reading "occasional" spikes in O2 levels in a gas pipeline, but initial investigation can not detect where they could be coming from, instrumentation technicians have stated that the instrument is working properly. What are typically causes (if any) of this kind of situations, Does anyone have any experience?

As much as possible, do it right the first time...

 

[zdas04]

I've seen this kind of thing when pig launchers/receivers were left isolated, but not purged. Over time, small leakage past the kicker/bypass or the barrel isolation valve can pressurize the barrel to pipeline pressure. When this happens, the barrel can reach maximum pipeline pressure, then when the pressure drops, the volume in the barrel can introduce the natural gas/air mix into the line. The oxygen readings are never very high, but they can pass detection level and spike an instrument.

When I was having this problem we started purging the launcher/receivers of air before completing the pigging evolution. Stopped having oxygen spikes on that line.

[bold]David Simpson, PE[/bold]
MuleShoe Engineering

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. Galileo Galilei, Italian Physicist

 

[engr2GW]

Thanks zdas04.
I assume the leaking, pressure build up and drop, and eventual sucking in of O2 happens at the barrel during normal operation? and the O2 is not introduced into the gas stream during pigging since O2 have (apparently) introduced into the barrel. That is a good point, and thank you.
I will look at that plus other possible causes.

As much as possible, do it right the first time...

 

[zdas04]

You open the barrel to remove the pig after the pig run. Once the pig is out you close the receiver up and shut the vent. Some people purge the barrel, before leaving, but many people don't. If you don't, then there is a barrel full of air and any valve leakage will pressurize it.

[bold]David Simpson, PE[/bold]
MuleShoe Engineering

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. Galileo Galilei, Italian Physicist